This invention relates generally to the field of microwave ovens and in particular to an improved rotating antenna system therefor.
In the field of microwave ovens, several methods have been used in attempting to achieve satisfactory distribution of microwave energy within the oven cavity. Some manufacturers have utilized so-called "reflective mode stirrers". With the "reflective mode stirrers", a reflective multi-bladed rotatable stirrer element is placed in the path of the incoming microwave energy and the stirrer is rotated either by directing a flow of air toward the blades or by a separate drive motor. The microwave energy is randomly deflected by the blades and is thus randomly distributed within the oven cavity. Microwave ovens which utilize mode stirrers often also use turntables for rotating the food during cooking so that the operator does not have to interrupt operation of the oven to manually reposition the food. The use of a turntable does result in substantial added cost to the manufacturer.
Another well known method of distributing microwave energy within the oven cavity and toward the food has been the use of a rotating antenna. One example of such an antenna is described in U.S. Pat. No. 4,284,868 issued on Aug. 18, 1981 to James E. Simpson. Simpson, in '868, discloses a 2.times.2 planar array of 1/2 wavelength radiators suspended below the top of the oven cavity and rotated by airflow circulated through the oven cavity.
Another example of a rotating antenna for a microwave oven is shown in U.S. Pat. No. 4,421,968 issued to John M. Osepchuk on Dec. 30, 1983. Osepchuk in '968 discloses an antenna which includes conductive strips positioned parallel to and less than 1/4 wavelength from an adjacent wall to reduce or eliminate radiation therefrom. Osepchuk '968 also provides a plurality of radiating elements at the ends of the conductive strips directed away from the adjacent wall for directing radiant energy toward the food load.
The prior art has thus included several constructions attempting to maximize the available microwave energy reaching the food load. These various methods have included mode stirrers for reflecting microwave energy and distributing it in a random manner, the use of a turntable with or without a mode stirrer in an attempt to eliminate manual turning of the food load, and rotating antennas for directing microwave energy toward the food load. There has been, however, no known showing of a rotating antenna system which utilizes a radiating center-fed dipole element having radiation modifiers for increasing the intensity of the microwave energy at the center of the oven cavity and for ensuring that the microwave energy extends uniformly outward from the center of the antenna as it rotates. The rotating antenna of the present invention further includes impedance balancing members associated with the dipole radiator for effectively matching the impedance of the source of energy with the impedance of the heating cavity.